The present disclosure relates to a secondary battery.
An ordinary secondary battery includes, for example, a current cut-off mechanism to prevent the secondary battery from being overcharged when it is charged. In a secondary battery disclosed in Japanese Unexamined Patent Application Publication No. 2014-137891, a current cut-off mechanism is formed by joining a cylindrically-shaped charge-collecting protrusion disposed in the upper end of a positive-electrode-side charge collector inside the battery to the top of a bowl-shaped reverse plate connected to a fastening member for enabling an external connection (i.e., a terminal). Further, a top plate part is disposed in the top of this charge-collecting protrusion with a fragile part interposed therebetween, and a through-hole for preventing a difference between a pressure in a gap formed between the reverse plate and the top plate part and a pressure inside the battery is formed in the top plate part.
In the above-described current cut-off mechanism, when the temperature of the battery rises during a charging process, a gas pressure inside the battery increases. As a result, the gas present inside the battery passes through the through-hole and pushes up the reverse plate, so that the reverse plate is bent backward, i.e., is bent upward. Consequently, the fragile part is ruptured and the top plate part, which is joined to the reverse plate, is detached from the charge-collecting protrusion. As a result, the positive-electrode-side charge collector disposed inside the battery is electrically cut off from the fastening member for the external connection.